The move will fuel fears that clients for the planned next generation of nuclear power plants could get drawn into an industrial relations battle.
Power plants and oil refinery works are usually covered by the “Blue Book” agreement for engineering construction.
But workers fear the Blue Book deal will be ripped-up next if major employers withdraw from the JIB.
One union source said: “If they are allowed to destroy the JIB agreement then the next logical step is to rip up the Blue Book.”
Demonstrators are now planning a protest organised by Unite outside the the Lindsey Oil Refinery in North Lincolnshire next Monday.
Unite regional officer Chris Weldon said: “The companies are trying to bulldoze their plans through by ripping up long-standing national agreements without any negotiation.”